1. Field of the Invention
This invention relates to a fixing apparatus for heating and fixing toner images on a transfer medium such as recording paper, and more specifically to a fixing apparatus applicable to such image producing equipment as electrophotographic copying machines and laser recording equipment and in which a transfer medium or recording paper with toner image on it is fed between a heat roller and a press roller, both in pressure contact with each other and rotating together, to fix the toner image.
The invention also relates to a copying machine with a paper feeding apparatus which feeds, one by one, the lowermost sheet of stacked recording papers with toner images fixed, and more specifically to an oil application apparatus in the copying machine which applies oil to the surface of the recording paper when the transferred image is fixed on the recording paper surface.
2. Description of the Prior Art
In recent years, a growing number of copying machines are using a document circulation apparatus to enable making fast plural copies of documents. The document circulation apparatus separates one sheet at a time from the stacked documents on a stacker, automatically feeds them onto the platen glass of the copying machine, and, after exposure processing, returns them to the stacker. This entire process is repeated.
In one processing cycle, the document circulation apparatus generates one set of copies, one copy for each sheet of the document. Thus, the documents are circulated the same number of times as the number of copies taken. Such an apparatus usually employs a "bottom-feed, return -to-top" system as a technique for separating and feeding each of the stacked documents. In this technique, the lowermost sheet of the document on the stacker is separated one at a time and fed to the image processing section and the exposed sheets are returned successively onto the top of the stacked document on the stacker. This process is repeated a required number of times.
Various types of automatic two-side copying machines have been proposed which automatically record the document images not only on one side of the recording paper but also on the other side. In such automatic two-side copying machines, the image processing section copies a document image on one side of the recording paper, and the copied paper is temporarily stacked on an intermediate stacker in the equipment and then again fed to the image processing section.
A plurality of recording paper sheets with document images copied on one side are stacked on a tray of the intermediate stacker, with the image side facing up. When the document feeding is started again, a pressing plate is lowered to press the stacked recording paper and at the same time a feed roll is rotated to feed the bundle of the recording papers toward a multiple feed prevention means, where the lowermost sheet of the stacked paper is separated by frictional action and again fed to the image processing section.
The bottom-feeding technique in which the lowermost sheet of the document or recording paper is separated and fed one by one is generally accomplished by a multiple feed prevention means which consists of a feed belt and a stop roller pressing against the feed belt to produce friction, which is used for sheet separation.
In the above document circulation apparatus, the documents are repetitively circulated through a series of processes, so that there are possibilities of the documents being folded, chipped away or wrinkled. And there are cases where important documents are torn. As a counter- measure, it is widely practiced that a copy is first taken and that this copy is used as a second document instead of the document and then stacked on the stacker for further processing. In the afore-mentioned "bottom-feed, return-to-top" method, however, there is a problem that since the toner-fixed surface of the lowermost sheet of the second document and the back of the second lowermost sheet are strongly pressed against each other, excess friction is produced resulting in the toner being scaled off and smearing the second document.
Also in the two-side copying there is a similar problem. That is, the recording paper sheet at the bottom of the stacked papers on the intermediate stacker is separated and fed one sheet at a time by the action of friction, so that toner is removed by excess friction, smearing the paper, as in the case where the second document is used.